An onboard information device can handle a variety of highly entertaining video and audio contents to make an occupant in a vehicle comfortable, and it has been becoming common to provide a plurality of AV (Audio Visual) devices in the vehicle for playing back the video and audio contents.
For example, as for an onboard display provided for a back seat occupant for viewing, it is mounted not only on the ceiling of the vehicle, but also on the back of the front seats sometimes. Alternatively, it is often mounted on each seat for exclusive use recently. In any of the foregoing mounting modes, to ensure convenience of a user, a wireless remote controller is employed for operating the onboard display. The remote controller can be placed in the remote control storage space of the onboard display so as to put it out of the way when the onboard display is not used.
The removable remote control of the onboard display often includes a light emitting element (like an LED: Light Emitting Diode) for illuminating buttons by considering cases of using it during night or in a comparatively dark environment.
To light the light emitting element for illuminating buttons with stability, it is necessary to send a rated current through it. Accordingly, to carry out luminance control of the light emitting element for illuminating buttons, pulse width modulation (PWM) control is essential which varies duty (ratio of ON/OFF of the pulse width) without varying the current (voltage) flowing through the light emitting element for illuminating buttons.
Thus, the conventional onboard information device such as an audio device having a light emitting element for illumination like an LED acquires from the vehicle a signal referred to as a rheostat signal with the duty corresponding to the luminance for controlling the luminance of the illumination, and carries out luminance control by converting it to a DC voltage corresponding to the duty and by applying it to the light emitting element for illumination like an LED (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Laid-Open No. 10-199683/1998.
As described above, to light the light emitting element for illumination like an LED with stability, it is necessary to employ the pulse width modulation that controls the luminance by varying the duty while causing the rated current to flow while fixing the applied voltage. According to the technique disclosed in Patent Document 1, to control the luminance of the light emitting element for illumination like an LED in response to the rheostat signal, it supplies the DC voltage corresponding to the rheostat signal from the onboard display side. Accordingly, when dimming the illumination (lowering the DC voltage), since the current value flowing through the light emitting element for illumination like an LED reduces, it is feared that unstable lighting state with luminance unevenness due to variation of the luminance can occur at low luminance.
Let us suppose that light emitting element like an LED is used for illuminating buttons of the remote controller. In this case, to acquire the rheostat signal and perform the duty variable control by the remote control itself, it must include a comparatively high-performance microprocessor, which will lead to a cost increase and is not practical.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a remote controller capable of reducing the variation of the luminance at low luminance, and of achieving the luminance control of the light emitting element for illuminating buttons with a comparatively low performance microprocessor.